The present invention(s) relate to measurement apparatus and methods, and more particularly to scanning probe microscopy apparatus and methods.
The fundamental understanding of nanoscale phenomena as well as its exploitation in device applications requires access to local properties. In recent years, a number of scanning probe based techniques, including scanning surface potential microscopy (SSPM), scanning spreading resistance microscopy (SSRM), and scanning capacitance microscopy (SCM), have been developed to access microscopic transport properties of nanoscale structures. (See S. V. Kalinin and D. A. Bonnell, in Scanning Probe Microscopy and Spectroscopy: Theory, Techniques and Applications, ed. D. A. Bonnell (Wiley VCH, New York, 2000, p. 205)). As processing of nanostructures becomes more sophisticated, there may be the potential to utilize complex materials such as nonlinear electronic, ferro and piezo electric, and ferromagnetic compounds.
In many complex materials multiple physical parameters are strongly coupled so that the complexity often takes on the form of nonlinear response to external excitations. For example, polycrystalline oxides and semiconductors exhibit non linear electrical behavior and capacitive coupling that are exploited in positive temperature coefficient of resistance, thermistors and varistors, and in solar cells. Nonlinear electro-mechanical properties in organic and inorganic ferroelectrics are used in memory devices and passive circuitry.
The incorporation of these and other materials at nanoscale dimensions has motivated the development of scanning probe microscopy (SPM) techniques and like techniques that access nonlinear properties. Conventional SPM techniques may be used for imaging and measuring various local properties of surfaces or materials on a small scale. SPM techniques typically work by measuring a local property—including mechanical properties such as height, electrical properties such as capacitance or impedance, magnetic properties, electrostriction, piezoelectric effect, or ferroelectric effect—with a probe tip placed very close to the sample. Often, the microscope raster-scans a probe over the sample while measuring the particular local property.
For example, in atomic force microscopy (AFM), a small tip on the end of a cantilever is moved across a surface. A vertical deflection of the cantilever by repulsive forces (in contact mode) indicates local height.
Also, piezoresponse force microscopy (PFM) is an SPM technique in which periodic bias is applied to a conductive tip in contact with a surface. The bias results in periodic surface displacement due to inverse piezoelectric effect or electrostriction of a ferroelectric surface. Mapping of the amplitude and phase of the displacement provides information of ferroelectric domain structures.
Various SPM tips having a conductive coating are commercially available from various suppliers. For any SPM mode, in which the tip is in contact with the surface, a conductive coating can be degraded due to mechanical wear or high current density in the tip-surface junction. (See P. Eyben, M. Xu, N. Duhayon, T. Clarysse, S. Callewaert, W. Vandervorst, J. Vac. Sci. Technol. B 20, 471 (2002))